Cable grips for drawing, holding and supporting electrical cables are well known in the art. These devices include a braided open wire mesh sleeve formed from interwoven metallic wire strands which may be expanded radially by longitudinal compression to enable them to readily receive the cable and radially contracted by longitudinal stretching to frictionally engage the periphery of the cable. Subsequently applied forces tending to separate the grip from the cable or to move the grip along the cable cause a firmer grip on the cable.
Examples of these prior art devices are disclosed in the following U.S. Pat. No. 1,807,993 to Martin; U.S. Pat. No.1,994,674 to Van Inwagen, Jr.; U.S. Pat. No. 2,112,281 to Ferris; U.S. Pat. No. 2,602,207 to Kellems; U.S. Pat. No. 2,766,501 to Kellems; and U.S. Pat. No. 3,551,959 to Mastalski.
Such devices are suitable for the fairly rugged electrical cable, but significant problems arise when the cable to be pulled is fragile. An example is fiber optic cable which comprises a flexible jacket encasing a single optical fiber or a bundle of optical fibers therein. Such fragile cable can be easily crushed or its optical characteristics can be distorted if the radial compressive forces on the cable are localized and become too great. Also, the optical fiber can be easily broken when subjected to excessive bending forces. In addition, it is typical to have pre-assembled on the end of fiber optic cable a fragile optical connector receiving one or a bundle of optical fibers therein and secured by epoxy and a crimp. Once again, this fragile connector is highly susceptible to crushing radial compressive forces as well as longitudinal tension forces which could easily snap the connector from the cable.
Moreover, fiber optic cable is much smaller in diameter than the typical electrical cable. These small diameters in most cases are much less than the conventional wire mesh grips can adequately hold. Also, the fiber optic connector at the end of the fiber optic cable has a much larger outside diameter than the cable so that a conventional grip selected to fit and adequately grip the cable cannot expand enough to accept the larger connector diameter. Conversely, a grip designed to receive the large diameter connector cannot compress enough to grip the smaller cable diameter. A typical example is a connector with a 0.5 inch outer diameter and a cable with a 0.073 inch outer diameter.
A method presently used to protect a fiber optic cable connector during pulling comprises wrapping the connector in a layer of foam rubber and then inserting this into a plastic sleeve which in turn is inserted into an oversized wire mesh grip. This method, however, is expensive and time consuming since conventional wire mesh grips are relatively stiff, thereby creating extreme difficulty in inserting the small and flexible cable with a connector attached. In addition, after assembly of this combination, the holding capability of the oversized wire mesh is marginal and may allow slippage of the cable and pull out of the pre-assembled connector.
In addition to these problems, a grip for pulling fiber optic cable must adequately grip the cable, accept any pre-assembled connectors, and not damage the cable or the connector during installation and pulling. There are four basic cable conditions that must be contended with. The first is a cable by itself, containing one or a plurality of optical fibers, or plural cables all without preassembled connectors. This provides only one rather uniform diameter for the grip to contend with.
A second condition comprises a single fiber optic cable with a pre-assembled connector, with both the cable and the connector diameter being within the grip diameter range so that the grip can be compressed longitudinally and therefore expand sufficiently in the radial direction to accept the combined cable and connector and also then be stretched longitudinally to thereby reduce the radius of the wire mesh into a sufficient gripping engagement of the cable.
A third cable condition comprises a single fiber optic cable with a pre-assembled connector where the connector size is beyond the expansion of the wire mesh that is made to suit the cable diameter.
Finally, the fourth basic cable condition comprises a plurality of fiber optic cables with pre-installed connectors where the connector diameter build-up is beyond the expansion capability of the wire mesh.